public void SubtractCounts(MailboxSizeTracker.FolderSizeRecord other)
 {
     this.MessageCount            -= other.MessageCount;
     this.TotalMessageSize        -= other.TotalMessageSize;
     this.DeletedMessageCount     -= other.DeletedMessageCount;
     this.TotalDeletedMessageSize -= other.TotalDeletedMessageSize;
     this.AlreadyCopiedCount      -= other.AlreadyCopiedCount;
     this.AlreadyCopiedSize       -= other.AlreadyCopiedSize;
 }
 private void UpdateFolderData(MailboxSizeTracker.FolderSizeRecord newRecord)
 {
     MailboxSizeTracker.FolderSizeRecord other;
     if (this.folderData.TryGetValue(newRecord.FolderId, out other))
     {
         this.totals.SubtractCounts(other);
     }
     this.totals.AddCounts(newRecord);
     this.folderData[newRecord.FolderId] = newRecord;
 }